EEVblog #536 - HP35670A DSA Repair

[vaualbus]

I think that the reason why the board haven't got the footprint is because this boards for agilent aren't troubleshooting so you have a fault and you replace it by paying thousends of dollars. Dave have you looked at this addition service manual contents?
LINK: h**p://www.home.agilent.com/upload/cmc_upload/All/35670-90067_supplement.pdf, there some more content in there. Probably the schematics will be avaible as soon as the instrument go out of production.
If you really want to repair it try to ask to agilent If they gave to you the schematics, somebody in the world should have those either a repair center or agilent itself.
Have you tried to put a signal in?
Apparently in new revision the instruments use only one cpu board, I've read that on the supplement manual somehere If I recall correct.
Best regards, Alberto

[N2IXK]

Do you have any evidence that the PSU was actually replaced?  Looked like some 1995 date codes on the caps, which dates the PSU to the same age as the rest of the instrument. Perhaps the $1600 was a repair estimate, not an amount actually spent on a failed repair?

Interesting that the DC input still works. Do the DC and AC primary portions of the PSU share the same switching transformer, with all the secondary side rectifiers and regulators in common?

[sleibson]

The 39.xxxx MHz crystal oscillator in this instrument is a wonder. It takes up a huge amount of board space! I would have guessed that with all the attention and space given it, this oscillator was supposed to be some sort of ultra-stable clock source for all of the spectral measurements this DSA is supposed to make, but then I would have expected an oven-controlled crystal if stability was that important.

My guess would be it's a Butler oscillator. How low drift and low phase noise it is I don't know. Probably not hugely special in the phase noise department given the low frequency measurements.
It could simply be a carry-over from an old design, before canned oscillators cut the mustard?

Well, I was using canned oscillators in the 1970s, predating this design by more than a decade.

--Steve

[Oracle]

how much did you pay for it? and how can a psu repair possible cost 1600$ ? what the hell did they do with it?

1600$ and they didn't fix anything... 

[GermanMarkus]

Dave, I think you missed the black AC fuse at the backside of the PSU!?

[magnus0re]

Nice going. maybe it's the same fault on the adc board.
Please make a followup soon

[ZekeD]

I'm hoping the I2 holds the ADC cal data tables, and with corrupt/missing cal data, the self test of the ADC's (and more..) is read as a fail. Now you have me wanting a DSA to muck around with.

Keep us posted. Great stuff.

[hikariuk]

how much did you pay for it? and how can a psu repair possible cost 1600$ ? what the hell did they do with it?

1600$ and they didn't fix anything... 

Official parts are often hilariously expensive compared to an identical non-official part, going by my experiences with IT related kit.  I don't know if $1,600 is plausible even then though (I've no idea what a PSU of that kind is really even worth; I'm just a curious proto-newbie).

[Stonent]

Well if it's complaining about gate arrays, I'd start looking at those Actel chips.

Pull them out one by one  and re-run the diags and see if there's a point where one chip is removed but the diags do not indicate any additional failures, that might indicate that Actel chip has died.  Also maybe check if there's any small GAL chips anywhere on the board.

[G7PSK]

Has it been exposed to some form of solvent, that would explain the melted rubber and the screen could also carry plastic into the ic sockets. highly informative on trouble shooting and I for one would love to see Dave carry on with the repair.

[grayfox386]

i would check the i2c eeprom for short it probably has config data for the adc on it if not that then check gate arrays

[ddavidebor]

Has it been exposed to some form of solvent, that would explain the melted rubber and the screen could also carry plastic into the ic sockets. highly informative on trouble shooting and I for one would love to see Dave carry on with the repair.

That's ugly melted thing melt itself with time. Hp loves it.

[zinkoxyde]

Dave, I recently got a Tektronix 2430a that failed a bunch of self tests with the ADCs and triggers. I ended up clearing the NVRAM and that took care of the problems. It must have gotten corrupted some how. I always blame software (or firmware in this case) before hardware.

[HWgeek]

Remember the old axiom - K.I.S.s   

If there was one bad regulator, there may be others, so then the chips that are powered up by other possibly blown regulators will show up as a fail too.   This certainly can be a great debug learning "series" for people who might be interested in what it takes to fix something electronic.

Here's hoping that you follow up with additional video(s) and mayhaps get the darn thing working!

[Napalm2002]

Amazing video I think Dave, I would very much like to see you go into further testing. I would say this vid has been one of my favs. Good luck on fixing it Dave! I think you should fix it up kinda no matter what the cost. Maybe some of us could donate parts to you or even start a fund my dsa fix video? Just a thought. I'm a huge Acdc fan by the way

[Fezder]

nice video, good that it eventually booted up

[iXod]

Before you cleaned it up I thought that the goo might have capacitively loaded down the oscillator circuit...

These repairs that end "not fully functional" are great! This is how many of us end up! And its great to see your process and choices you make.

The end? result is really secondary...